The influence of convection and temperature on the radiation impedance of an open duct termination exhausting a hot gas is commonly described by a complex theory. A simplified analytical expression is proposed for low frequencies. Both models assume a free jet with uniform velocity bounded by infinitely thin shear layers. The convective velocity that should be assumed when applying these models to a non-uniform outflow is uncertain. A simplified version of the so-called Vortex Sound Theory demonstrates that the convective velocity one should assume is lower than the jet centerline velocity. © 2014 Acoustical Society of America.
Hirschberg, A., & Hoeijmakers, P. G. M. (2014). Comments on the low frequency radiation impedance of a duct exhausting a hot gas. Journal of the Acoustical Society of America, 136(2), EL84-EL89. https://doi.org/10.1121/1.4885540